Waterproof paper negative



Feb. 13, 1962 C. J. MURPHY, JR., ETAL WATERPROOF PAPER NEGATIVE Filed March 1'7, 1958 EMULSION PA PER GEORGE EL. WOOD COR/VEL/US l. MURPHY J!- INVENTORS 3,2LZM Patented Feb. 13, 1962 3,021,214 WATERPROGF PAPER NEQATEVE Cornelius J. Murphy, In, and George F. 1.. Wood, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New .l'ersey Filed Mar. 1'7, 1958, Ser. No. 721,733 13 Claims. ((Il. 9685) This invention concerns a water-proof photographic paper base for use as a paper negative.

In the photographic processes in which the photographic print is obtained from the camera by a process of contacting the paper negative against the finished paper stock and using a pod to supply the processing chemicals, it is desirable to have a paper base which is water-proof in order to provide good dimensional stability. When some papers have been used for the negative in this type of process, a defect termed gulley streak occurs as a wavy line of lower density in a length-wise direction on the positive print. This defect has been found to be due to a diiference in the rate of expansion between the negative and positive sheets during pod processing.

The water-proofing of photographic paper is well known employing various polymeric materials in latex form. For instance, a latex composed of a mixture of emulsion polymerized styrene and butadiene, polystyrene and gelatin is shown in US. 2,760,864 issued August 28, 1956. However, this is not a pigmented coating but is a water-proofing coating applied over a baryta coated paper. If the baryta were incorporated in the latex, the product would not be waterproof. Also several coats are necessary which results in a relatively expensive operation.

It would not be possible to use the same type of paper for a paper negative, as used for a positive, since it would be undesirable to have a high degree of reflection of incident light after it had passed through emulsion. Moreover, the use of gelatin with many latex mixtures results in agglomeration of the particles and some mixtures are not entirely satisfactory for coating smoothly. In addition, the water-proofness of various papers shown in the prior art using latex type coatings has not been sufficient to provide the dimensional stability required in the process or to eliminate gulley streaks.

Adhesion of a photographic emulsion to latex coated paper is a problem with many of the papers which are known, and for that reason, these papers would be unsatisfactory for use as a paper negative in a diffusion type photographic process.

We have discovered a one coat process for coating paper base for use as a paper negative which provides satisfactory adhesion to the photographic emulsion, supplies good dimensional stability, has a low reflective index, and is relatively inexpensive.

One object of this invention is to provide a water-proof paper negative for use in a diffusion type photographic process. Another object is to provide a pigmented waterproof photographic paper base using a latex based coating composition. A further object is to provide a coating composition which water-proofs paper base and provides good adhesion to a light sensitive silver halide emulsion.

The above objects are obtained by coating a mixture of a styrene-butadiene copolyrner and polystyrene mixed with casein, carbon black and titanium dioxide. This coating is then overcoated with a gelatino-silver halide emulsion. In using the paper negative provided according to my invention, the exposed paper is contacted against the paper positive with the developer solution in jelly form between the two contacting surfaces. The use of this type negative surprisingly results in an increase in the efifective resolving power of the system.

An advantage of our coating system is that only a single coat is required since this coat Waterproofs the paper, contains pigments for preventing halation, and does not require an additional subbing coating. Moreover, in addition to lowered costs, this one coat system has the added advantages of being less prone to emulsion cracking and emulsion pressure desensitization when coated with the type of emulsion used in the diffusion type process.

In the accompanying drawing, the single figure is a sectional view of a photographic paper negative containing a photographic emulsion, a coating comprising titanium dioxide, carbon black, a styrene-butadiene copolymer, polystyrene and casein.

In order for a paper negative to be satisfactory for use in the diffusion type process, the base should have a maximum Cobb size value of 0.10 gram. Below in Table I is a list of Cobb size values for various bases.

Table I Cobb size values (a) A typical baryta coating consisting of a gelatin to BaSO ratio of 1:10 0330+ (b) A plasticized baryta coating consisting of a latex to BaSO ratio of 1:10 0.220 (c) A typical waterproof coating (non-pigmented) of cellulose acetate butyrate 0.050 (d) A typical waterproof coating (non-pig mented) of styrene-butadiene latex 0.010 (e) A non-pigmented white coating of cellulose acetate 0.135

(f) Grey pigmented waterproof coating consisting of styrene-butadiene latex. (The coating which is shown in Table II is the preferred coating) 0.01-0.09

The Cobb size values for various bases are expressed in terms of the number of grams of water absorbed by 100 square centimeters of base surface in 5 minutes. The above bases a-e were measured with a pH of 7. The paper negative base f was tested with a water solution at a pH of 12 which is the pH of the jelly developer used in practice. These conditions are more severe than plain water and values using plain water on the base would be slightly lower than those reported above.

In order to successfully carry out our invention the following values in Table II must be used:

The proportions of total styrene and butadiene in the latex are:

Usable Preferred Range Proportions (Solids Basis) Styrene: Butadieue (Polyinerized form including polystyrene) 1.74:1.00 1.61.0 to

Resins containing styrene-butadiene copolymers which can be used are those with butadiene-styrene copolymer ratios of :20,.70:30, 67:30, 65:35 and 60:40..

The following example illustrates one embodiment of our invention but is not intended to limit it in any way:

A roll of 19.5 lbs. per 1,000 sq. ft. photographic base stock was coated with a 20 g. per sq. meter coat of a pigmented resin latex coating. The coating was prepared by dispersing 55 g. titanium dioxide, 0.61 g. of carbon black and 13.1 g. casein in 191 g. water. To this dispersion was added 238 g. of a latex mixture containing 145 g. styrene-butadiene resin latex combination (60:40: of butadienezstyrene) and 93 g. polystyrene resin latex. After mixing the latex with the pigment and the casein, the mixture was coated on the surface of the paper. The resin latex coating after drying was passed in front of a bank of infrared heaters at such a rate as to maintain the coated paper at a temperature of 290 F. for /2 minute in order to fuse the surface of the coating.

The 238 g. of latex mixture refers to the total dry solids. The styrene-butadiene latex is 48% solids in the dispersion and the polystyrene is 49% solids.

The coated paper having the fused latex coating thereon was cooled and a panchromatic sensitized gelatino silver halide emulsion was coated over the waterproofed paper base. The sensitized negative paper was then exposed and developed while being contacted against the surface of a paper positive having thereon a photo sensitive layer and containing therein a suitable nucleating agent. The developer was a jelly type developer having a pH of about 12. The image transferred from the negative to the positive indicated that better resolving power was obtained than when using a white paper negative and also better than that obtained using a similar paper negative with gelatin as the binder instead of the polystyrenestyrene-butadiene resin latex. The waterproof coating before coating with the silver halide emulsion had a reflection density of 0.57.

In our preferred embodiment the titanium dioxide is treated with a wetting agent and dispersed in water prior to the addition of the vehicles (casein and latex). Carhon black is then added. A casein solution is prepared at a temperature of 160 F. and added to the titanium dioxide dispersion, after which the styrene-butadiene copolymer latex and polystyrene latex can be added either simultaneously or separately, although it is preferred to add the styrene-butadiene latex prior to adding the polystyrene.

The coating may be applied using various conventional coating methods such as the dip coater, brush coater, air-brush coater (or air-knife coater), extrusion or hopper coater, or the like. Various temperatures may be used for coating, but a temperature somewhat above room temperature, about 80 F., is preferred.

After coating the paper, it is dried using any conventional drying equipment and then passed before radiant heaters at which time the coating is fused so that a continuous waterproof film is formed. The temperature of the surface of the paper is within the range of 270- 290 F. for /2% minutes.

It will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of our invention. For instance, the coated paper may be calendered in order to decrease the bulk and to produce a smoother surface.

The temperature at which the coating is fused may be varied from 250300 C. with appropriate variations in time.

This paper negative surprisingly produces superior results over those known and used previously since the resolving power is improved as well as the dimensional stability.

The amount of carbon black which we incorporate in our pigmented coating is that required to give a reflection density of 0.30 to 1.50. Within this range the negative has improved resolving power compared to coatings having reflection densities outside of this range.

Typical diffusion photographic processes are illustrated in US. Patents 2,435,717, 2,435,718, 2,500,421, 2,563,342 and many others. However, it will be evident that modifications may be made in the process such as using a jelly developer instead of a liquid and the like without affecting the operation of our process.

In one embodiment of our invention, grey paper stock is used for coating with our pigmented coating. How-- ever, White paper or paper containing a color may also be used.

We claim:

1. A process for preparing a photographic paper negative for use in a photographic diffusion process comprising the successive steps of preparing a coating composition by first wetting a titanium dioxide material and dispersing it in water, adding a casein solution prepared at a temperature of about F. to the titanium dioxide dispersion, adding a latex consisting of a styrene-butadiene copolymer and polystyrene so that the solids content of the coating composition contains 44.3-49,2% of the copolymer and 28.7-31.8% polystyrene, and coating the mixtureonto a paper base, drying, fusing at a temperature of 250-300 F., cooling and coating with a photographic gelatin emulsion containing light-sensitive: silver salts.

2. A process for making a photographic paper negative for use in a photographic diffusion process comprising preparing a water dispersion of titanium dioxide, casein, carbon black, polystyrene and styrene-butadiene copolymer in which from 44.3-49.2% is a styrene butadiene resin latex and 28.7 to 31.8% polystyrene resin latex, and coating on a paper base, drying, heat treating at a temperature of 250-300 F. and coating with a photographic silver halide emulsion.

3. An aqueous coating composition comprising :15- 23% titanium dioxide, 06% carbon black, 44.3-49.2% styrene-butadiene copolymer, 28.7-31.4% polystyrene and 3.8-4.2% casein, by weight solids basis.

4. An aqueous coating composition comprising 15- 23% titanium dioxide, '0-6% carbon black, 38-42% casein, and a styrene-butadiene copolymer and polystyrene latex so that 44.3-49.2% of the coating composition is styrene-butadiene copolymer, and 28.7- 31.4% is polystyrene by weight solids basis.

5. A paper support for a photographic paper negative for use in a diffusion type photographic process comprising a paper support having thereon a coating comprising 15-23% titanium dioxide, 0-6% carbon black, 44.3- 49.2% styrene-butadiene copolymer, 28.7-31.4% polystyrene, and 38-42% casein by weight.

6. A paper support for a photographic paper negative for use in a diffusion type photographic process comprising a gray paper support having thereon a coating comprising l5-23% titanium dioxide, 0-6% carbon black, 44.349.2% styrene-butadiene copolymer, 28.731.4% polystyrene, and 3.8-4.2% casein by weight.

7. A paper support for a photographic paper negative for use in a diffusion type photographic process comprising a white paper support having thereon a coating comprising 15-23% titanium dioxide, 0-6% carbon black, 44.3-49.2% styrene-butadiene copolymer, 28.7-3l.4% polystyrene, and 38-42% casein by weight.

8. A photographic paper negative for use in a diffusion type photographic process comprising a paper sup port having thereon a coating comprising 15-23% titanium dioxide, 0-6% carbon black, 44.3-49.2% styrenebutadiene copolymer, 28.7-3l.4% polystyrene, and 38-42% casein by weight, and having coated thereon a light-sensitive silver halide emulsion.

9. A photographic negative paper for use in a diffusion type photographic process comprising a white paper support having thereon a coating comprising 1523% titanium dioxide, 0-6% carbon black, 44.3-49.2% styrenebutadiene copolymer, 28.7-31.4% polystyrene, and 3.8- 42% casein by weight and having coated thereon a lightsensitive silver halideemulsion.

10. A photographic negative paper for use in a difiusion type photographic process comprising a gray paper support having thereon a coating comprising 1523% titanium dioxide, 06% carbon black, 44.3-49.2% styrenebutadiene copolymer, 28.7-31.4% polystyrene, and 3.84.2% casein by weight and having coated thereon a light-sensitive silver halide emulsion.

11. A paper support for use in a difiusion type photographic process comprising a paper support having thereon a pigmented coating having a reflective density of 0.30 to 1.50 comprising 15-23% titanium dioxide, 0-6% carbon black, 44.349.2% styrene-butadiene copolymer, 28.7-31.4% polystyrene, and 3.8-4.2% casein by weight, and having coated thereon a light-sensitive silver halide emulsion.

12. A paper support for use in a diffusion type photographic process comprising a white paper support having thereon a pigmented coating having a reflective density of 0.30 to 1.50 comprising 15-23% titanium dioxide, 06% carbon black, 44.349.2% styrene-butadiene copolymer, 28.73l.4% polystyrene, and 3.84.2% casein, and having coated thereon a light-sensitive silver halide emulsion.

13. A paper support for use in a diffusion type photographic process comprising a gray paper support having 6 thereon a pigmented coating having a reflective density of 0.30 to 1.50 comprising 15-23% titanium dioxide, 0-6% carbon black, 44.3-49.2% styrene-butadiene copolymer, 28.731.4% polystyrene, and 3.8-4.2% casein, and having coated thereon a light-sensitive silver halide emulsion.

References Cited in the file of this patent UNITED STATES PATENTS 2,462,534 Murray Feb. 22, 1949 2,597,087 Cowgill May 20, 1952 2,686,764 Geister Aug. 17, 1954 2,698,235 Swindells Dec. 28, 1954 2,731,434 Johnson Jan. 17, 1956 2,750,349 OHerren June 12, 1956 2,756,150 Griggs et al. July 24, 1956 7 2,784,088 Griggs Mar. 5, 1957 2,801,938 Iler Aug. 6, 1957 2,805,160 Griggs et a1. Sept. 3, 1957 OTHER REFERENCES July 

5. A PAPER SUPPORT FOR A PHOTOGRAPHIC PAPER NEGATIVE FOR USE IN A DIFFUSION TYPE OF PHOTOGRPAHIC PROCESS COMPRISING A PAPER SUPPORT HAVING THEREON A COATING COMPRISING 15-23% TITNAIUM DIOXIDE, 0-6% CARBON BLACK, 44.349.2% STYRENE-BUTADIENE COPOLYMER, 28.7-31.4% POLYSTYRENE, AND 3.8-4.2% CASEIN BY WEIGHT. 